1. Field of the Invention
This invention relates generally to refrigeration and air conditioning systems, and is more particularly directed to a flow control apparatus for regulating the flow of refrigerant between the condenser and the evaporator of a refrigeration system.
2. Description of the Background Art
Generally, large commercial air conditioning systems include a chiller which consists of an evaporator, a compressor, and a condenser and a throttling device. Usually, a heat transfer fluid is circulated through heat transfer tubing in the evaporator to transfer heat from the heat transfer fluid to refrigerant in the evaporator. The heat transfer fluid chilled in the evaporator tubing is normally water or glycol, which is circulated to a remote location to satisfy a cooling load. The refrigerant in the evaporator evaporates as it absorbs heat from the heat transfer fluid, and the compressor operates to extract and compress this refrigerant vapor, and to discharge the compressed vapor to the condenser. In the condenser, the refrigerant vapor is condensed and the liquid refrigerant is delivered back to the evaporator through the throttling device, where the refrigeration cycle begins again.
Lubrication systems for providing oil to the bearings and rotors in the compressor are typically included in the air conditioning systems. Commonly, the oil exits the compressor with the discharge refrigerant to an oil separator which is typically disposed between the compressor and the condenser. After the oil is separated from the refrigerant by the separator, the refrigerant is passed to the condenser and the oil is returned to the compressor.
In certain refrigeration systems no mechanical oil pump is used to supply the necessary oil pressure to the compressor. Consequently, the compressor relies upon the system differential pressure between the condenser and evaporator to pump the oil to the rotors and bearings. As a minimum amount of oil pressure is required to supply sufficient quantities of oil for lubrication and cooling, there may be operating conditions imposed on the machine where the system pressure differential is not large enough to supply an adequate oil flow. Since the system pressure differential is set by the temperature difference between the condenser water and the evaporator water, insufficient oil pressure results when these temperatures approach each other. This situation commonly occurs during a system start-up. However, this situation may also occur at other steady state operating conditions.
Additionally, as condensed refrigerant flows to a lower sump portion of the condenser it must be metered out the evaporator. A flow control unit is needed which ensures that only condensed refrigerant liquid, as opposed to refrigerant vapor, passes to the evaporator. In other words, the control unit should maintain a liquid seal during operation of the system to improve system efficiency.
One approach to this is described in U.S. Pat. No. 5,285,653 granted to Steven E. Meloling, et. al., Feb. 15, 1994. In that patent, the control apparatus includes a standpipe that extends upwardly from an outlet of a condenser sump, with a number of vertical openings spaced about the cylindrical wall of the standpipe near its lower end. A cylindrical metering sleeve is disposed within the cylindrical standpipe.
A ring-shaped float is fitted over the standpipe and attached to the cylindrical metering sleeve so as to close off the standpipe openings when the level of the refrigerant liquid is below a minimum level. As the refrigerant level rises, the float rises with it, and causes the cylindrical metering sleeve to uncover the openings. This allows more refrigerant to flow through to subsequent stages. However, this arrangement does not provide a satisfactory solution to the abovementioned pressure differential problem.
It is desirable to have a refrigerant control apparatus which increases efficiency by both providing an artificially imposed pressure differential between the condenser and the evaporator and by ensuring that only condensed refrigerant liquid passes to the evaporator.